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Change-Id: I49ce97136c17173c4ae3965c694af6e7bc49897d

1 files changed, 229 insertions, 0 deletions

diff --git a/src/org/jivesoftware/smack/util/DNSUtil.java b/src/org/jivesoftware/smack/util/DNSUtil.java
new file mode 100644
index 0000000..628d8e8
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+++ b/src/org/jivesoftware/smack/util/DNSUtil.java
@@ -0,0 +1,229 @@
+/**
+ * $Revision: 1456 $
+ * $Date: 2005-06-01 22:04:54 -0700 (Wed, 01 Jun 2005) $
+ *
+ * Copyright 2003-2005 Jive Software.
+ *
+ * All rights reserved. Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jivesoftware.smack.util;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+import java.util.SortedMap;
+import java.util.TreeMap;
+
+import org.jivesoftware.smack.util.dns.DNSResolver;
+import org.jivesoftware.smack.util.dns.HostAddress;
+import org.jivesoftware.smack.util.dns.SRVRecord;
+
+/**
+ * Utility class to perform DNS lookups for XMPP services.
+ *
+ * @author Matt Tucker
+ */
+public class DNSUtil {
+
+    /**
+     * Create a cache to hold the 100 most recently accessed DNS lookups for a period of
+     * 10 minutes.
+     */
+    private static Map<String, List<HostAddress>> cache = new Cache<String, List<HostAddress>>(100, 1000*60*10);
+
+    private static DNSResolver dnsResolver = null;
+
+    /**
+     * Set the DNS resolver that should be used to perform DNS lookups.
+     *
+     * @param resolver
+     */
+    public static void setDNSResolver(DNSResolver resolver) {
+        dnsResolver = resolver;
+    }
+
+    /**
+     * Returns the current DNS resolved used to perform DNS lookups.
+     *
+     * @return
+     */
+    public static DNSResolver getDNSResolver() {
+        return dnsResolver;
+    }
+
+    /**
+     * Returns a list of HostAddresses under which the specified XMPP server can be
+     * reached at for client-to-server communication. A DNS lookup for a SRV
+     * record in the form "_xmpp-client._tcp.example.com" is attempted, according
+     * to section 14.4 of RFC 3920. If that lookup fails, a lookup in the older form
+     * of "_jabber._tcp.example.com" is attempted since servers that implement an
+     * older version of the protocol may be listed using that notation. If that
+     * lookup fails as well, it's assumed that the XMPP server lives at the
+     * host resolved by a DNS lookup at the specified domain on the default port
+     * of 5222.<p>
+     *
+     * As an example, a lookup for "example.com" may return "im.example.com:5269".
+     *
+     * @param domain the domain.
+     * @return List of HostAddress, which encompasses the hostname and port that the
+     *      XMPP server can be reached at for the specified domain.
+     */
+    public static List<HostAddress> resolveXMPPDomain(String domain) {
+        return resolveDomain(domain, 'c');
+    }
+
+    /**
+     * Returns a list of HostAddresses under which the specified XMPP server can be
+     * reached at for server-to-server communication. A DNS lookup for a SRV
+     * record in the form "_xmpp-server._tcp.example.com" is attempted, according
+     * to section 14.4 of RFC 3920. If that lookup fails, a lookup in the older form
+     * of "_jabber._tcp.example.com" is attempted since servers that implement an
+     * older version of the protocol may be listed using that notation. If that
+     * lookup fails as well, it's assumed that the XMPP server lives at the
+     * host resolved by a DNS lookup at the specified domain on the default port
+     * of 5269.<p>
+     *
+     * As an example, a lookup for "example.com" may return "im.example.com:5269".
+     *
+     * @param domain the domain.
+     * @return List of HostAddress, which encompasses the hostname and port that the
+     *      XMPP server can be reached at for the specified domain.
+     */
+    public static List<HostAddress> resolveXMPPServerDomain(String domain) {
+        return resolveDomain(domain, 's');
+    }
+
+    private static List<HostAddress> resolveDomain(String domain, char keyPrefix) {
+        // Prefix the key with 's' to distinguish him from the client domain lookups
+        String key = keyPrefix + domain;
+        // Return item from cache if it exists.
+        if (cache.containsKey(key)) {
+            List<HostAddress> addresses = cache.get(key);
+            if (addresses != null) {
+                return addresses;
+            }
+        }
+
+        if (dnsResolver == null)
+            throw new IllegalStateException("No DNS resolver active.");
+
+        List<HostAddress> addresses = new ArrayList<HostAddress>();
+
+        // Step one: Do SRV lookups
+        String srvDomain;
+        if (keyPrefix == 's') {
+            srvDomain = "_xmpp-server._tcp." + domain;
+        } else if (keyPrefix == 'c') {
+            srvDomain = "_xmpp-client._tcp." + domain;
+        } else {
+            srvDomain = domain;
+        }
+        List<SRVRecord> srvRecords = dnsResolver.lookupSRVRecords(srvDomain);
+        List<HostAddress> sortedRecords = sortSRVRecords(srvRecords);
+        if (sortedRecords != null)
+            addresses.addAll(sortedRecords);
+
+        // Step two: Add the hostname to the end of the list
+        addresses.add(new HostAddress(domain));
+
+        // Add item to cache.
+        cache.put(key, addresses);
+
+        return addresses;
+    }
+
+    /**
+     * Sort a given list of SRVRecords as described in RFC 2782
+     * Note that we follow the RFC with one exception. In a group of the same priority, only the first entry
+     * is calculated by random. The others are ore simply ordered by their priority.
+     * 
+     * @param records
+     * @return
+     */
+    protected static List<HostAddress> sortSRVRecords(List<SRVRecord> records) {
+        // RFC 2782, Usage rules: "If there is precisely one SRV RR, and its Target is "."
+        // (the root domain), abort."
+        if (records.size() == 1 && records.get(0).getFQDN().equals("."))
+            return null;
+
+        // sorting the records improves the performance of the bisection later
+        Collections.sort(records);
+
+        // create the priority buckets
+        SortedMap<Integer, List<SRVRecord>> buckets = new TreeMap<Integer, List<SRVRecord>>();
+        for (SRVRecord r : records) {
+            Integer priority = r.getPriority();
+            List<SRVRecord> bucket = buckets.get(priority);
+            // create the list of SRVRecords if it doesn't exist
+            if (bucket == null) {
+                bucket = new LinkedList<SRVRecord>();
+                buckets.put(priority, bucket);
+            }
+            bucket.add(r);
+        }
+
+        List<HostAddress> res = new ArrayList<HostAddress>(records.size());
+
+        for (Integer priority : buckets.keySet()) {
+            List<SRVRecord> bucket = buckets.get(priority);
+            int bucketSize;
+            while ((bucketSize = bucket.size()) > 0) {
+                int[] totals = new int[bucket.size()];
+                int running_total = 0;
+                int count = 0;
+                int zeroWeight = 1;
+
+                for (SRVRecord r : bucket) {
+                    if (r.getWeight() > 0)
+                        zeroWeight = 0;
+                }
+
+                for (SRVRecord r : bucket) {
+                    running_total += (r.getWeight() + zeroWeight);
+                    totals[count] = running_total;
+                    count++;
+                }
+                int selectedPos;
+                if (running_total == 0) {
+                    // If running total is 0, then all weights in this priority
+                    // group are 0. So we simply select one of the weights randomly
+                    // as the other 'normal' algorithm is unable to handle this case
+                    selectedPos = (int) (Math.random() * bucketSize);
+                } else {
+                    double rnd = Math.random() * running_total;
+                    selectedPos = bisect(totals, rnd);
+                } 
+                // add the SRVRecord that was randomly chosen on it's weight
+                // to the start of the result list
+                SRVRecord chosenSRVRecord = bucket.remove(selectedPos);
+                res.add(chosenSRVRecord);
+            }
+        }
+
+        return res;
+    }
+
+    // TODO this is not yet really bisection just a stupid linear search
+    private static int bisect(int[] array, double value) {
+        int pos = 0;
+        for (int element : array) {
+            if (value < element)
+                break;
+            pos++;
+        }
+        return pos;
+    }
+}
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